1. Exercise
1 2
Evaluate xy when x = 7 and y = 8. 28

2. Exercise
ab 2
Evaluate
when a = 18 and b = 12.
108

3. Exercise
1 2
Evaluate (c + d)f
when c = 3, d = 4, and f = 10. 35

4. Exercise
r 2
Evaluate (s + t)
when r = 7, s = 5, and t = 4.
31.5

6. A B C D

7. D A B C

8. Formula: Area of a Triangle
1 2
A = bh

9. Altitude
An altitude is a segment drawn from any vertex of a triangle perpendicular to the line containing the opposite side.

10. A C B A C B C A B

11. C A B

12. A C B D A C B D A C D B

13. Example 1
Find the area of ∆XYZ.
324 cm2

14. Example
What is the area of a triangle with b = 12 units and h = 9 units?
54 units2

15. Example
If the base of a triangle is 10 units and its area is 100 units2, what is its height?
20 units

16. Example
If the height of a triangle is equal to its base, what is its height if its area is 72 units2?
12 units

17. Example What is the area of the triangle below? 27.125 units2 3 4 8 a

18. Example What is the length of altitude a in the triangle below?8 7 a
3 4
units

19. b2 h b1

20. b2 b1 h b1 b2

21. Formula: Area of a Trapezoid
A = (b1 + b2)h
The area of a trapezoid (A) is half the sum of the bases (b) times the height (h).
1 2

22. Example 2
Find the area of the trapezoid.
13 cm
8 cm
18 cm
124 cm2

23. Example
What is the area of a trapezoid with b1 = 8 units, b2 = 11 units, and h = 6 units?
57 units2

24. Example
If the longer base of a trapezoid is twice the shorter base, its height is 8 units, and its area is 48 units2, what is the length of each base?
4 units and 8 units

25. Example
Find the area of the shaded triangle. 12 6 3
9 units2

26. Example
Find the area of the shaded trapezoid. 16 10 5
60 units2